1. The mechanism of thymic determination of MHC restriction of T lymphocytic antigen recognition. 2. Extrathymic influences on the T cell repertoire. 3. T Cell influence on immunoglobulin class-switch by B cells. 4. HTLV transformation of B lymphocytes. 5. Clonal analysis of the immune response to a murine retrovirus-associated lymphoma. 6. Examination of the T lymphocyte repertoire by generation of T cell clones from radiation-induced bone marrow chimeras.